1. Field of the Invention
The present invention relates to a stabilizer for chlorine-containing polymers and to a process for the preparation thereof. More specifically, the invention relates to a stabilizer for chlorine-containing polymers, which can be favorably blended into a chlorine-containing polymer, imparts excellent thermal stability and exhibits suppressed moisture re-absorption tendency, as well as to a process for the preparation thereof. The invention is further concerned with effectively utilizing, as a stabilizer, waste clay discharged in the step of refining fat or oil.
2. Prior Art
When exposed to the heat and light, chlorine-containing polymers such as vinyl chloride resins cause hydrochloric acid to be removed from the molecular chains thereof and undergo decomposition and discoloration. In order to stabilize vinyl chloride resins against the thermal decomposition, a variety of stabilizers and stabilizer compositions have heretofore been proposed and have been put into wide use.
Among such stabilizers, a variety of siliceous compounds have been used as inorganic stabilizers.
According to Japanese Patent Publication No. 32899/1977, a chlorine-containing polymer is blended with, as a heat stabilizer, a silicate such as synthetic calcium silicate which contains in the pores thereof an organic blending agent, and according to Japanese Laid-Open Patent Publication No. 15237/1992, a chlorine-containing polymer is blended with a fine crystalline calcium silicate hydrate.
Silicate particles such as calcium silicate particles exhibit good dyeing property, and can be excellently blended and dispersed into the resin, and further react with hydrogen chloride and with chlorine ions to trap them. However, these silicates are hydrophilic. This tendency becomes conspicuous when the silicates are in an amorphous form or in a fine crystalline form exhibiting excellent reactivity with hydrogen chloride.
That is, the siliceous compounds generally absorb water during the storage, and releases water when they are kneaded together with a chlorine-containing polymer causing the blended resin composition to be foamed.
Siliceous compound is rarely used by itself as a heat stabilizer and is generally used in combination with various organic blending agents. However, the siliceous compound is hydrophilic and is poorly compatible with hydrophobic organic components such as higher fatty acid salts.
In the step of refining fats or oils, furthermore, waste clay containing fats or oils in relatively large amounts is by-produced arousing a problem in regard to its disposal. If the waste clay can be effectively utilized, then it is greatly meaningful from the standpoint of preventing environmental pollution and effective utilization of resources.